This invention relates to the field of voice transformation or voice morphing with encoded information. In particular, the invention relates to voice transformation for preventing fraudulent use of modified speech.
Voice transformation enables speech samples from one person to be modified so that they sound as if they were spoken by someone else. There are two types of transformations:                Modify the voice without a specific target. For example, lowering the pitch by some constant amount.        Modify the voice so it will sound as close as possible to a target speaker.        
There are many uses for voice transformation. The following are some examples:                Film dubbing. This allows one actor to dub several voices in a film and also allows dubbing in different languages while maintaining the original actor voice.        Telecom services. Various services allow a caller to modify his voice. For example, sending a birthday greeting to a child with his favorite cartoon character or a celebrity voice.        Toys. Voice transformation can be used in games and toys for generating various voices. For example, a parrot like doll that repeats what is being said to it in a parrot voice.        Music industry. Voice transformation tools such as the AUTO-TUNE tool (AUTO-TUNE is a trade mark of Antares Audio Technologies) have become very popular in the music industry.        Online chat. Chatting text and SMS (Short Message Service) can be converted into speech with a voice that is similar to the sender's voice.        Gaming. This allows online game players to speak with the voice of their online avatar instead of their own voice.        
However, in the wrong hands voice transformation tools can also be used improperly. Examples of improper use include the following                Impersonating another person without his consent.        Voice disguising while performing illegal act to avoid identification.        
At present, it is usually possible to distinguish between a natural and transformed voice and it is not possible to mimic fully a different speaker. However, as research progresses it is expected that within a few years the quality of voice transformation system might be high enough to be indistinguishable from natural voice and indistinguishable from a copied speaker.